bank solution

Author: SophieDeBenedetto

lessons/otp-concurrency/simple_bank/lib/simple_bank.ex

@@ -59,7 +59,21 @@ defmodule SimpleBank do
   end
 
   @spec withdrawl(pid(), String.t(), pos_integer()) :: {:ok, {pos_integer(), pos_integer()}} | {:error, reason}
-  def withdrawl(bank_pid, account_id, amount) do
+  def withdrawl(bank_pid, account_id, amount) when is_integer(amount) and amount > 0 do
+    case get_account_by_id(bank_pid, account_id) do
+      nil -> {:error, :missing_account}
+      account ->
+        if account.balance < amount do
+          {:error, :insufficient_funds}
+        else
+          account = GenServer.call(bank_pid, {:withdrawal, account, amount})
+          {:ok, account.balance}
+        end
+    end
+  end
+
+  def withdrawl(_bank_pid, _account_id, amount) when is_integer(amount) and amount <= 0 do
+    {:error, :pos_integer_only}
   end
 
   def init(initial_state) do
@@ -90,10 +104,20 @@ defmodule SimpleBank do
     {:reply, account, new_state}
   end
 
+  def handle_call({:withdrawal, account, amount}, _from, state) do
+      account = do_withdrawal(account, amount)
+      new_state = update_account_in_state(account, state)
+    {:reply, account, new_state}
+  end
+
   def do_deposit(account, amount) do
     Map.put(account, :balance, account.balance + amount)
   end
 
+  def do_withdrawal(account, amount) do
+    Map.put(account, :balance, account.balance - amount)
+  end
+
   def update_account_in_state(account, state) do
     accounts = Enum.reject(state, fn a -> a.id == account.id end)
     [accounts | account]

lessons/otp-concurrency/simple_bank/test/simple_bank_test.exs

@@ -45,15 +45,15 @@ defmodule SimpleBankTest do
 
   describe "withdrawl/3" do
     test "decreases the account balance by the withdrawn amount", %{bank: bank_pid}  do
-      assert {:ok, 100} == SimpleBank.withdrawl(bank_pid, "test_id", 10)
+      assert {:ok, 90} == SimpleBank.withdrawl(bank_pid, "test_id", 10)
     end
 
     test "does not negative ammount balances", %{bank: bank_pid}  do
-      assert {:error, :insufficient_funds} == SimpleBank.withdrawl(bank_pid, "test_id", -1)
+      assert {:error, :insufficient_funds} == SimpleBank.withdrawl(bank_pid, "test_id", 1000)
     end
 
     test "does not allow withdrawls of negative amounts", %{bank: bank_pid}  do
-      assert {:error, :pos_integer_only} == SimpleBank.withdrawl(bank_pid, "test_id", 1000)
+      assert {:error, :pos_integer_only} == SimpleBank.withdrawl(bank_pid, "test_id", -1)
     end
 
     test "raises an error if the account does not exist", %{bank: bank_pid}  do